The present invention relates to a manufacturing method of a magnetic material for metallic thin film magnetic recording media and a metallic thin film magnetic recording medium.
Known well typically hitherto is a coated magnetic recording medium manufactured by coating a magnetic paint obtained from dispersing a pulverized magnetic material such as oxide magnetic powder or alloy magnetic powder into an organic binder such as vinyl chloride-vinyl acetate group copolymer, polyester resin, urethane resin, polyurethane resin or the like on a nonmagnetic support and drying the same.
On the other hand, in accordance with an increase in requirement for high-density magnetic recording, proposed to a general attention is a so-called metallic magnetic thin film type magnetic recording medium with a metallic magnetic material such as Co--Ni alloy, Co--Cr alloy, Co--O or the like adhered directly onto a nonmagnetic support such as polyester film or the like by means of vacuum thin film formation through plating, vacuum evaporation, sputtering, ion plating or the like.
These metallic magnetic thin film type magnetic recording media are superior in coercive force, squareness ratio or the like, and are then not only superior in electromagnetic conversion characteristic at short wavelengths but also advantageous to have merits that a loss of thickness to arise at the time of record demagnetizing and playback is considerably minimized because the thickness of magnetic layers can be extremely thinned, and that a charging density of magnetic materials can be enhanced because a binder or nonmagnetic material need not be mixed into the magnetic layers.
Further, in case where a magnetic layer is formed for improving an electromagnetic conversion characteristic of the metallic magnetic thin film type magnetic recording medium, thereby obtaining larger outputs, a so-called diagonal vapor coating whereby the magnetic layer is coated diagonally has already been developed.
The diagonal vapor coating has realized superior magnetic characteristic and electromagnetic conversion characteristic by using only the vaporization component diagonally incident from shutting off the vapor by means of a shutter, mask or the like.
However, the diagonal vapor coating is not necessarily preferable to allow a vapor of the magnetic material onto a nonmagnetic support at 10 to 20% at most at the time of vaporization, thus resulting in an unsatisfactory availability of the magnetic material. Consequently, a reduction in cost of the magnetic material is required in this case.
Still further, as disclosed in Japanese Patent Unexamined Publication No. 63-195234 and Japanese Patent Unexamined Publication No. 7-54069, generally an evil influence is quite unavoidable on the vaporized magnetic material in magnetic characteristic and electromagnetic conversion characteristic after formation of a thin film due to the quantity of impurities contained therein such as carbon, Al, Mn, oxygen and others, therefore a considerably severe requirement is given to the purity thereof.
For example, in the case where a vapored tape is fabricated by means of Co alloy as a magnetic material, it is known that the quantity of oxygen contained in the Co alloy may exert an influence on a stability of the magnetic material at the time of vapor deposition and a tape characteristic such as dropout or the like, and thus it is necessary for securing the tape characteristic that the oxygen content in the Co alloy be minimized as low as possible.
For this end, various techniques such as vacuum melting, addition of deoxidizer at the time of melting and the like have ever been taken as a means available for removing oxygen forcedly when the Co alloy is molten. Then, the addition of deoxidizer may be pointed out particularly as an effective means, however, the large quantity of remaining deoxidizer may exert an evil influence on the tape characteristic, therefore a selection of means for removing oxygen in the Co alloy has been regarded as important.
However, to employ such means as will enhance the purities is fundamentally to increase number of processes, thus leading to a higher costing. Further, if the material of high purity is used from the beginning as hitherto, a higher costing of the raw material will be incidental thereto, and an increase in the number of processes and a higher costing of the raw material are both unavoidable in consequence, thus leading to a rise of the tape cost.
Still further, it is conceivable that a low purity of cobalt working as a raw material be used as a means for suppressing the cost of Co alloy as low as possible. However, since an impurity or sulfur above all is contained much in the cobalt of low purity, a crack is capable of arising during working at the time of melting, and a deterioration of workability results inevitably therefrom to uselessness after all.